The following relates to the diagnostic arts. It is described with particular reference to example embodiments that relate to imaging of rare cells, such as epithelial cells, in the buffy coat of a centrifuged blood sample. However, the following relates more generally to apparatuses and methods for handling test tubes of various types, and to analysis systems employing same.
In the technique of quantitative buffy coat analysis, a whole blood sample is drawn and processed using anti-coagulant additives, centrifuging, and so forth to separate the blood into components including a buffy coat component comprised principally of white blood cells. Rare cells of interest which are present in the buffy coat, such as certain epithelial cells associated with certain cancers, are tagged using a suitable fluorescent dye, and fluorescence microscopic imaging is then used to count the fluorescent dye-tagged cells of interest. Quantitative buffy coat analysis is a promising non-invasive technique for screening for certain cancers, for monitoring cancer treatment, and so forth.
In conventional microscopy, a sample slide is prepared by disposing a biological fluid or other sample of interest on a planar microscope slide and optionally covering the sample with a cover glass. The prepared slide is placed onto a microscope stage and secured thereto by clips, a vacuum chuck, or so forth. An arm or other mount positions the objective of the microscope in close, focused proximity to the sample on the microscope stage. The sample stage is typically translatable in two transverse “x” and “y” directions lying in the plane of the sample stage to enable scanning of the area of the planar sample. Because the focus depth of the microscope objective is typically small, the slide and sample stage should be highly planar, and the translation should be precisely within this plane. Existing microscope stages provides sufficient planarity to enable large-area scanning without re-focusing of the objective, or with limited refocusing.
For quantitative buffy coat analysis, applying conventional microscopy calls for extracting the buffy coat layer from the centrifuged test tube for placement onto the planar microscope slide. However, extraction of the buffy coat from the centrifuged test tube can be difficult because the buffy coat layer is a thin layer of the centrifuged sample sandwiched between much thicker layers of packed red blood cells and of plasma.
In another approach, the buffy coat is expanded in the test tube for more accurate visual or optical measurement by placing a plastic cylinder, or float, into the tube. The float has a density which is less than that of red blood cells (1.090 g/ml) and greater than that of plasma (1.028 g/ml) and occupies nearly all of the cross-sectional area of the tube. The volume-occupying float, therefore, generally rests on the packed red blood cell layer and greatly expands the axial length of the buffy coat layers in the tube for analysis. In such an approach, the test tube itself in effect serves as a annular microscope slide.
It will be appreciated that such a cylindrical microscope slide does not comport with a conventional x-y translatable planar microscope slide stage. Scanning of the annular microscope slide calls for relative rotation of the test tube about its axis and relative translation of the test tube along the test tube axis. It is difficult to perform such complex scanning while simultaneously keeping the region of interest at a substantially constant distance from the microscope objective.